test: check every mapping the library writes by alexander-akait · Pull Request #297 · webpack/webpack-sources

alexander-akait · 2026-09-26T15:11:54Z

Summary

The test suite used to validate every mapping the library wrote, through test/__mocks__/createMappingsSerializer.js. That check had silently stopped running:

the mock was never loaded, because its jest.requireActual("../createMappingsSerializer") path doesn't exist;
it wrapped the serializer's default export, but getFromStreamChunks and streamAndGetSourceAndMap now write through createMappingsWriter.

#292 removed the file as dead code. This PR brings the check back for the current writer.

test/helpers/validate-mappings.js replaces the module's createMappingsWriter export before any library file loads, so every writer the library creates validates each mapping:

generated positions only move forward: line, then column within a line;
a segment without a source (sourceIndex === -1) has no original position or name;
a segment with a source has valid original fields.

A stream that breaks these rules now fails the test that produced it. Without the check, it's encoded into a quietly wrong mappings string. For example, a source that streams line 1 column 5 and then column 2 through ConcatSource.map() returns "KAAA" without the check, silently dropping the second mapping, and throws with it.

One file serves both runners: node --test loads it with --require in the test, test:coverage and test:update-snapshots scripts, and Jest loads it with setupFiles.

What kind of change does this PR introduce?

test

Did you add tests for your changes?

The change is a test harness check. Verification:

Suite passes with the check: all 89,973 tests, including the Fuzzy combinations, under node --test on Node.js 22, Jest 30 on Node.js 20, and Jest 27 on Node.js 16 and 10. The library's current output is valid.
One unit test adjusted: a test in test/helpers-unit.js fed the writer a synthetic stream whose source-less segments carried original positions, which the library never produces. Those segments now use -1 like the library does. The test still compares writer and serializer output, and still forces the writer's buffer to grow.
The check fires in both runners: against the old synthetic stream, it fails that test under both node --test and Jest.
npm run lint, npm run fmt:check and npm run test:coverage pass. Coverage still counts only lib/.

Does this PR introduce a breaking change?

No, only tests change.

If relevant, what needs to be documented once your changes are merged or what have you already documented in this PR?

Nothing.

Use of AI

Claude Code found the dead mock while moving the tests to node:test and wrote this replacement.

🤖 Generated with Claude Code

https://claude.ai/code/session_01ThsbPWvW5vnYWEaFs2Q22F

Generated by Claude Code

`test/__mocks__/createMappingsSerializer.js` validated each mapping, but it was never loaded, and it wrapped the serializer's default export, which the library no longer uses: `getFromStreamChunks` and `streamAndGetSourceAndMap` write through `createMappingsWriter`. #292 removed it as dead code. `test/helpers/validate-mappings.js` brings the check back for the writer. It replaces the module's `createMappingsWriter` export before any library file loads, so every writer checks that mappings come in generated order and that a segment without a source has no original position or name. A stream that breaks that now fails the test that produced it instead of being encoded into a quietly wrong `mappings` string. `node --test` loads it with `--require`, Jest with `setupFiles`, so one file serves both. The whole suite passes with the check. The one exception was a unit test feeding the writer a synthetic stream whose source-less segments carried original positions; those segments now use -1 like the library does. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01ThsbPWvW5vnYWEaFs2Q22F

changeset-bot · 2026-09-26T15:11:58Z

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coderabbitai · 2026-09-26T15:12:03Z

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linux-foundation-easycla · 2026-09-26T15:12:05Z

✅ Unknown (21d4a87)
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alexander-akait · 2026-09-26T15:12:20Z

EasyCLA is red because it can't match the Claude co-author trailer on this commit to a GitHub account. That can't be fixed from the branch and needs a maintainer override, as on #292 and #293. Nothing else is failing so far.

Generated by Claude Code

codecov · 2026-09-26T15:15:15Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.09%. Comparing base (5a9b34d) to head (21d4a87).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #297   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files          27       27           
  Lines        6318     6318           
  Branches      807      806    -1     
=======================================
  Hits         6261     6261           
  Misses         56       56           
  Partials        1        1

Flag	Coverage Δ
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codspeed · 2026-09-26T15:21:40Z

Merging this PR will degrade performance by 26.74%

⚠️

Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 7 improved benchmarks
❌ 16 regressed benchmarks
✅ 189 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
❌	Memory	`clear-cache memory: shared modules (no visited set — allocates per chunk)`	6.6 KB	72.8 KB	-90.94%
❌	Memory	`size-only-source memory: new SizeOnlySource()`	58.9 KB	436.1 KB	-86.49%
❌	Memory	`replace-source memory: construct + 100 insertions`	38.1 KB	136.6 KB	-72.13%
❌	Memory	`compat-source memory: delegated source() + map() through wrapper`	9.9 KB	31 KB	-68.19%
❌	Memory	`replace-source memory: source() concatenates result`	37.7 KB	84.1 KB	-55.18%
❌	Memory	`source-map-source memory: new SourceMapSource(simple)`	1.4 KB	2.6 KB	-46.27%
❌	Memory	`cached-source memory: warm sourceAndMap() returns cached references`	209 B	369 B	-43.36%
❌	Memory	`concat-source memory: source() concatenates children`	189.8 KB	302.2 KB	-37.19%
❌	Memory	`concat-source memory: map({ columns: true }) composes child maps`	3 MB	4.3 MB	-30.97%
❌	Memory	`source-map-source memory: sourceAndMap({ columns: true }) (combined inner)`	1.7 MB	2.5 MB	-30.39%
❌	Memory	`concat-source memory: new ConcatSource(...children)`	4.3 KB	5.5 KB	-21.99%
❌	Memory	`compat-source memory: new CompatSource(sourceLike)`	1.3 KB	1.7 KB	-21.23%
❌	Memory	`replace-source memory: map({ columns: true }) splices mappings`	2.4 MB	2.9 MB	-17.4%
❌	Memory	`source-map-source memory: map({ columns: true })`	1.3 KB	1.5 KB	-16.33%
❌	Memory	`raw-source memory: new RawSource(string)`	1.3 KB	1.5 KB	-16.33%
❌	Memory	`prefix-source memory: source() allocates rewritten string`	1.9 KB	2.2 KB	-11.43%
⚡	Memory	`prefix-source memory: new PrefixSource()`	14.9 KB	2.2 KB	×6.8
⚡	Memory	`original-source memory: new OriginalSource()`	4.3 KB	2.1 KB	×2.1
⚡	Memory	`clear-cache memory: shared modules (visited set — single allocation)`	1,384 B	912 B	+51.75%
⚡	Memory	`cached-source memory: construct from cachedData (no warm-up)`	784 B	544 B	+44.12%
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing claude/update-deps-github-actions-5ydose (21d4a87) with main (5a9b34d)}

alexander-akait · 2026-09-26T15:22:40Z

CodSpeed Performance Analysis is red, but the regression doesn't come from this PR. The PR changes only test/, jest.config.js and the test scripts in package.json. It doesn't touch lib/ or benchmark/, and the benchmark scripts (npm run benchmark / benchmark:memory) don't load test/helpers/validate-mappings.js. So the benchmarked code is identical to main.

CodSpeed also flags "Different runtime environments detected" for this comparison. Its biggest deltas are memory benchmarks that allocate once, for example new SizeOnlySource() going from 58.9 KB to 436.1 KB. That is the same cross-host noise noted on #293. No fix is needed here; a maintainer can acknowledge the report on CodSpeed. I can't re-run the CodSpeed check from this session.

Generated by Claude Code

alexander-akait merged commit d3548f7 into main Sep 26, 2026
35 of 37 checks passed

alexander-akait deleted the claude/update-deps-github-actions-5ydose branch September 26, 2026 15:45

alexander-akait mentioned this pull request Sep 26, 2026

ci: make the CodSpeed memory benchmarks deterministic #298

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Merging this PR will degrade performance by 26.74%

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